1. Field of the Invention
The present invention relates to a transformer and, more particularly, to a transformer accommodated in a case body of reduced size.
2. Discussion of the Related Art
High voltage spark lamps, such as metal halide lamps, have been employed as light source lamps for motor vehicles. The starters of these lamps incorporate transformers to provide an electrical power supply. FIGS. 6 and 7 show an example of a conventional transformer.
As shown in FIG. 6, a transformer 60 comprises a primary bobbin 62, a secondary bobbin 64, and cores 65. A primary coil 61 is wound around the primary bobbin 62, and a secondary coil 63 is wound around the secondary bobbin 64. Also, cores 65 are fitted into the secondary bobbin 64.
The primary bobbin 62 has a tubular body of nearly rectangular shape with the hollow inside portion serving as an arrangement portion 66 to accommodate the secondary bobbin 64 and the secondary coil 63. The primary coil 61 is wound around the primary bobbin 62 at the center thereof. Both ends of the primary coil 61 respectively constitute primary terminals 67, each projecting downwards as shown in FIG. 6.
The secondary bobbin 64 also has a tubular body of nearly rectangular shape with an axially extending hole 68 to receive the cores 65. Both ends 69 of the secondary bobbin 64 in the axial direction constitute flanges that extend outward. The distance defined by outer edges of the flanges 69 is substantially equivalent to the length of the primary bobbin 62 in the axial direction thereof.
The outer cross-section of each of the flanges 69 is identical in shape to the inner cross-section of the primary bobbin 62. However, the size of the outer cross-section of the flanges 69 is slightly smaller than the size of the inner cross-section of the primary bobbin 62. As shown in FIG. 6, at each lower end of the flanges 69, terminal forming portions 70 are formed in the axial direction of the secondary bobbin 64 but in opposite directions such that they are separate from each other. Secondary terminals 71 are formed at respective terminal forming portions 70 to project in the same direction as the respective terminal forming portions 70. The secondary coil 63 is wound around the secondary bobbin 64 except the flanges 69. Both ends of the secondary coil 63 are connected to the secondary terminal portions 71, respectively.
Referring to FIG. 6, the cores 65 comprise base portions 72 that extend vertically, projecting portions 73 the project from the respective upper ends of the base portions 72 in the direction to reduce the distance therebetween, and inner fitting portions 74 that project from the lower ends of the base portions 72 in the same direction as the respective projecting portions 73. The distance defined by the base portions 72 and the corresponding edges of the projecting portions 73 is equal to the distance defined by the base portions 72 and the corresponding edges of the inner fitting portions 74. Then, the length obtained by adding each length of the projecting portions 73 in the projecting direction is made equivalent to the length of the secondary bobbin 64 in the axial direction. The inner fitting portions 74 are shaped to be received into the fitting hole 68 of the secondary bobbin 64.
The assembly of the conventional transformer 60 will now be described.
The secondary bobbin 64 is inserted into the arrangement portion 66 of the primary bobbin 62 in the axial direction until the flanges 69 are positioned corresponding to both ends of the primary bobbin 62. The inner fitting portions 74 of the cores 65 are inserted into the fitting hole 68 from both axial ends of the secondary bobbin 64 that has been inserted into the arrangement portion 66 until one front surface of the inner fitting portion 74 abuts against the other front surface of the corresponding inner fitting portion. Concurrently, both front surfaces of the projecting portions 73 will also abut when the front surfaces of the inner fitting portions 74 abut.
As shown in FIG. 7, a cover 75 is fitted with the above-described transformer 60 to enclose the primary bobbin 62 and the secondary bobbin 64. When cover 75 is fitted with the transformer 60, the primary terminals 67 formed at both ends of the primary coil 61 project in the same direction through insertion holes formed in the cover 75. The secondary terminals 71 of the secondary bobbin 64 also project from the cover 75 outwards in the direction perpendicular to the projecting direction of the primary terminals 67.
The transformer 60 having the cover 75 is then accommodated in a case body 76 having an opening at one side such that the respective terminals 67, 71 are connected to the corresponding contacts (not shown) or corresponding contacts for connection to a discharge lamp (not shown) in a ballast 77 also accommodated in the case body 76. The opening of the case body 76 is covered with a lid (not shown) to seal the case body 76.
The transformer 60 is accommodated in the case body to face the ballast 77 accommodated in the case body 76 such that the secondary terminals 71 extend in the direction X--X and the primary terminals 67 extend in the direction Y--Y (perpendicular to the X--X direction) as shown in FIG. 7.
In the aforementioned conventional transformer 60, the secondary terminals 71 of the secondary bobbin 64 project in the same direction as the axial direction of the secondary bobbin 64. That is, the secondary terminals 71 project in the X--X direction which is perpendicular to the projecting direction of the primary terminals 67 as shown in FIG. 7. This structure keeps the secondary terminals 71 from being in contact with the primary bobbin 62 when inserting the secondary bobbin 64 into the arrangement portion 66 of the primary bobbin 62.
Therefore, the length of the case body 76 in the X--X direction must be large enough to accommodate the projecting secondary terminals 71. Also, the length of the case body 76 in the Y--Y direction must be large enough to accommodate the projecting primary terminals 67. As a result, the size of the case body 76 is enlarged.